HR: 1330h
AN: B12A-0757    [PDF]
TI: Identification of a Possible Second, Large Propagator North of the Hess Deep Rift
AU: * Smith, D K
EM: dsmith@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA 02543 United States
AU: Klein, E M
AF: Duke University, Division of Earth and Ocean ciences, Durham, NC 27708 United States
AU: Williams, C M
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA 02543 United States
AU: Zhu, W
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA 02543 United States
AB: The ridge-ridge-ridge triple junction at the northern edge of the Galapagos microplate is located at 2 40'N, where the Incipient Rift (IR) intersects the East Pacific Rise (EPR). The IR is north and west of Hess Deep and is a slowly diverging (15 mm/yr full-rate) spreading center separating the Cocos and Galapagos plates (the IR was first identified by P. Lonsdale and co-workers). In August, 2002, we mapped and sampled a broad area centered on the IR, including its intersection with the EPR and its apparent termination about 75 km to the east. Seabeam 2000 bathymetric and side-scan (amplitude) data, surface-towed magnetic data, imagery from 14 camera tows, and rock samples (53 dredges, 5 wax cores) and MAPR and CTD data were collected (results to be described by Klein et al. 2003 and Hanna et al. 2003). Seabeam bathymetry data collected to the northeast of the IR on our transit to port revealed a surprising result: a series of prominent NW/SE striking lineations, interpreted as faults, were mapped on about 1.5 My old crust. These faults are not evident in the satellite altimetry data. The faults dip to the NE and have throws of up to 500 m. We conducted a brief (aprox. 6 hr) Seabeam survey of the region to obtain a clearer idea of what the faults represent. Based on our limited survey, the faults appear to be the southern boundary of a west-pointing, v-shaped gore (similar orientation as the Hess Deep and IR gores). Our survey did not reveal matching faults on the northern boundary of the gore, but instead an abrupt transition from east-west lineations likely associated with Cocos-Nazca spreading to north-south abyssal hill lineations inherited from the EPR. A swath of multibeam data was collected for us by G. Christeson in August 2003, just to the east of our survey, and shows NE/SW lineated topography intersecting the northern boundary of the Galapagos gore. We infer that this newly mapped feature was a relatively large propagating rift that became inactive about 1 My ago. At that time the propagator associated with Hess Deep became the single dominant propagator in the region and the IR was formed. The existence of this second, perhaps larger propagator to the northeast of the IR emphasizes the complicated nature of the microplate boundaries in this region.
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology and bottom photography
SC: Biogeosciences [B]
MN: 2003 Fall Meeting